1. Field of the Invention
The present invention relates to a method and device for controlling the stroke of the ram of a press machine which moves in the vertical direction by means of a hydraulic cylinder, and, in particular, to a method and device for controlling the stroke of a press machine so that the operation of the press machine can be performed at high efficiency with low vibration and low noise.
2. Description of the Prior Art
An application for a method of controlling the stroke of the ram of a press machine has previously been made by the present applicant (Japanese Patent Application No. 61-25282), and the method of controlling the stroke of the ram of a press machine is known from laid open publication No. 62-183910.
A punching operation carried out by a press machine depends on the material of the workpiece, the plate thickness, and the punching velocity, but a large amount of noise and vibration are created in any cases.
For example, observations made on a turret punch press show that the vibration at a position 1 m away from the punch is about 75 dB, and at 10 m about 58dB. There is almost a linear relationship for the vibration in the interval between these points. In addition, the noise has been measured at about 98 dB at 10 m from the punch center and about 75 dB at 40 m. There is almost a linear relationship for the noise between these points.
This vibration and noise is produced by the friction between the stroke operating section and the plate material, and due to the deflection of the frame during the action of the stroke operating section. The greater the velocity of the stroke, the greater the amount of vibration and noise.
However, the control level for noise and vibration are determined by region and time of day, depending on the environmental control standards. Accordingly, the use of a press machine with a stroke operating section is severely restricted by time of day and by region, and in regions where the control is very strict it is necessary to provide elaborate anti-noise and antivibration devices.
Therefore, in the abovementioned previously known technology, technology is disclosed for carrying out a high efficiency process with low vibration and low noise by adjusting punching speed.
However, the principle by which vibration and noise are generated in the punching process is very complicated, and the appropriate value for the punching speed can only be obtained by actual observations. Accordingly, the appropriate value for the punching speed has been determined conventionally from test punch operations for type of material being processed, plate thickness and shape, or for each unit action. Accordingly, in the conventional technology, considerable time and trouble is required to create the appropriate speed and the overall operating efficiency is lowered.
In addition, conventional punch presses are constructed with the objective of performing the punching process. It is therefore difficult to perform a drawing process with such equipment.
However, in the case where one sheet of plate material contains a plurality of sections for drawing, and in the case where one sheet of plate material contains a mixture of sections for punching and sections for drawing, it is desirable to perform this drawing operation on a punch press.